18 :)

SELECT * FROM gallery2 WHERE topic_id="450831" UNION SELECT * FROM gallery2 WHERE topic_id="1059386" UNION SELECT * FROM gallery2 WHERE topic_id="80598" UNION SELECT * FROM gallery2 WHERE topic_id="1310795" UNION SELECT * FROM gallery2 WHERE topic_id="1702105" UNION SELECT * FROM gallery2 WHERE topic_id="398251" UNION SELECT * FROM gallery2 WHERE topic_id="1581594" UNION SELECT * FROM gallery2 WHERE topic_id="1690667" UNION SELECT * FROM gallery2 WHERE topic_id="42597" UNION SELECT * FROM gallery2 WHERE topic_id="265196" UNION SELECT * FROM gallery2 WHERE topic_id="1018035" UNION SELECT * FROM gallery2 WHERE topic_id="539073" UNION SELECT * FROM gallery2 WHERE topic_id="1484870" UNION SELECT * FROM gallery2 WHERE topic_id="1177419" UNION SELECT * FROM gallery2 WHERE topic_id="657612" UNION SELECT * FROM gallery2 WHERE topic_id="619278"